research years in california analyzed data on 15,000 older adults in areas with high particulate matter in the air. they did worse on cognitive studies. this is the first large study to show an association with brain function. as you plan your winter vacation, do not forget to pack a helmet. a new review of research confirms using a helmet when skiing and snowboarding decreases the risk and severity of head injuries. doctors say some complain it reduces visibility and may create a false sense of security. their studies find most severe head injuries on the slopes happened when skiers were not wearing helmets. a preliminary study suggesting eating more fish could help to reduce the risk of postpartum depression. researchers in canada say there is evidence that women's levels of omega three fatty acids and decrease during pregnancy and remain low six weeks after birth. more research needs to be done, but most dietitians a gree -- agree americans need to boost their intake of healthy fatty acids. >> tragedy in texas. federal investigators are trying to piece together how they train crashed